Absolute rate constants for reactions of free radicals in the high-temperature photolysis of formamide vapor. Part I. Carbamyl radicals

✍ Scribed by T. Yokota; R. A. Back

• Publisher: John Wiley and Sons
• Year: 1973
• Tongue: English
• Weight: 503 KB
• Volume: 5
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550050104

✦ Synopsis

The photolysis of formamide vapor at 2062 has been studied in a flow system with results essentially similar to those obtained previously under static conditions and higher conversions. The rotating-sector technique has been applied to the radical-chain decomposition of formamide under conditions (305"C, 1 1.5 tom) such that decomposition of the carbamyl (NHzCO) radical was rate controlling, so that [NHICO] >> [NH,]. A rate conslant of (3.1 +1.0) x lO'O(M.sec)-'was obtained for bimolecular chain termination by carbamyl radicals. A concurrent first-order radical loss, probably at the surface, was taken into account by the treatment described by Shepp. Both oxamide and HNCO were tentatively identified as termination products, suggesting the occurrence of both combination and disproportionation, 2NH2CO + NH2CO.CO.NH2

• HNCO + NHZCHO but quantitative estimates of the relative rates were not possible. From the rate constant for chain termination, and relative rate constants obtained previously, Arrhenius parameters A , = (5.9 + 2.0) X 1012sec-' and A0 = (1.04 f 0.35) X 10" (M.sec)-' were estimated for the unimolecular decomposition of carbamyl radicals in the high and low pressure limits.